1. Field of the Invention
The present invention relates to the formation of structures in microelectronic devices such as integrated circuit devices. More particularly, the invention relates to the formation of vias, interconnect metallization and wiring lines using multiple low dielectric constant intermetal dielectrics.
2. Description of The Related Art
In the production of microelectronic devices, integrated circuits utilize multilevel wiring structures for interconnecting regions within devices and for interconnecting one or more devices within the integrated circuits. In forming such structures, it is conventional to form a first lower level wiring lines, then an interlevel dielectric layer and then to form second level wiring lines. One or more metal filled vias are typically formed in the interlevel dielectric to connect the first and second level wiring lines.
One conventional method for forming a two level wiring structure is to first form a two level interconnect structure over a substrate. The surface of a substrate may be the surface of a silicon device structure or the surface of substrate may be an insulating layer. An oxide layer is typically deposited over the substrate by chemical vapor deposition. The first level interconnect structures are defined by a conventional photolithography process which forms openings through the oxide layer where the first level interconnects will be formed. Generally, the openings expose portions of conductors in the substrate to which interconnects are formed. The openings are filled with a metal interconnect to form the interconnect and form a metal plug. Then a layer of metal such as aluminum is deposited over the surface of the oxide layer and over the metal plug to a thickness appropriate for second level wiring lines. The metal layer is then patterned into the second level wiring lines. The second level wiring lines are defined in a conventional photolithography process by providing a layer of photoresist over the metal layer, exposing the photoresist through a mask and removing portions of the exposed photoresist layer to form a photoresist etch mask. The portions of the metal layer exposed by openings in the photoresist mask are then removed by etching and the photoresist mask is removed by ashing. After the two level interconnect structure is formed, it is necessary to provide an intermetal dielectric (IMD) layer between the second level wiring lines and covering the second level wiring lines to accommodate further processing of the integrated circuit device. In the past, the intermetal dielectric layer might consist of one or more layers of oxide deposited by plasma enhanced chemical vapor deposition or other processes.
Prior art integrated circuits produced by single or dual damascene processes with Cu interconnects and low dielectric-constant (k) intermetal dielectrics have used only one kind of low-k dielectric, either inorganic, organic or a hybrid of these two kinds. This conventional approach of using the same kind of low-k dielectric for both metal-level and via-level IMD's has limited process integration and implementation options. As a result, additional processing steps and added cost are required. It is desirable whenever possible to reduce the number of processing steps required to form a device because reducing the number of processing steps shortens the time required to produce the device and because eliminating processing steps improves yields and so reduces costs.
The present invention uses two or more dissimilar low-k dielectrics for the intermetal dielectrics of Cu-based dual damascene backends of integrated circuits. The use of both organic and inorganic low-k dielectrics offers several advantages due to the significantly different plasma etch characteristics of these two kinds of dielectrics. One dielectric serves as an etchstop in etching the other dielectric. No additional oxide or nitride etchstop layer is required. High performance is achieved due to the lower parasitic capacitance resulting from the use of low-k dielectrics.